An existing electric vehicle typically has two drive axles, and each drive axle is used for driving a pair of wheels located at opposite sides of the vehicle. Each drive axle receives a driving force provided by a drive electric motor arranged at the front or the rear of the vehicle. According to the number and the positions of the drive axles driven by the drive electric motor, the electric vehicle may achieve front-wheel drive, rear-wheel drive or four-wheel drive.
For a vehicle with a larger carrying capacity, for example, a large or heavy passenger bus or truck, its chassis is generally provided with more drive axles, for example, four axles, six axles or eight axles. The driving structure of such a vehicle is complex, and thus corresponding eight-wheel drive, twelve-wheel drive or sixteen-wheel drive are more difficult to achieve. Due to the limitation of the electric energy storage technology of the existing electric vehicle, when considering the necessary power demands and the endurance mileage, such a vehicle typically employs a fuel engine as a direct power source, instead of being driven by a drive electric motor as in the electric vehicle.
Chinese patent application No. 201310467918.2 of the applicant provides a power system for a series hybrid electric vehicle. The power system allows the use of alternative fuels with lower energy density instead of using traditional gasoline or diesel, and allows an engine in an auxiliary power unit to work in a working condition area in which both oil consumption and emission are very low, thereby effectively reducing the emission, improving the economic efficiency of the fuels, and compensating for the problem that the energy conversion efficiency of the power system of the series hybrid electric vehicle is relatively low. Moreover, the power system can be flexibly provided with an appropriate number of engines for combined use according to demands. Thus, through the combined use of a sufficient number of engines, electric power sufficient to meet the demands of the vehicle with a larger carrying capacity, for example a truck, can be provided by using cheap fuels, thereby providing possibility for an electric driving mode of such a vehicle.
For the existing electric vehicle employing the drive electric motor, wheels on opposite sides of one axle are generally driven by one drive electric motor, which is not conducive to the flexibility of the controlling of the electric vehicle. Another solution for the existing electric vehicle is to employ an in-wheel motor, but the cost is high, and because of the limitation on the provided power, it is merely applied to vehicles with a small carrying capacity, such as family cars.